The present invention relates to a method of making a semiconductor device such as a semiconductor chip provided with bump electrodes.
Recently, there is an increasing demand for mounting electronic components on a printed circuit board or on a ceramic board at high densities. As a method which meets such a demand, much attention is focused on bear chip mounting of semiconductor chips. In bear chip mounting, face-down mounting or flip-chip bonding is increasingly used instead of conventional face-up mounting. In the face-up mounting, wire-bonding is utilized to provide electrical connection between a semiconductor chip and a wiring pattern on a board. In the face-down mounting and the flip-chip bonding, a semiconductor chip having bump electrodes is mounted on a wiring board while providing connection between the bump electrodes and electrodes on the wiring board.
FIGS. 11a-13c illustrate an example of prior art method for making a semiconductor chip or semiconductor device having bump electrodes.
Firstly, in the prior art method, on a semiconductor substrate 60 as shown in FIG. 11a, a conductor film 63 for electroplating is formed, as shown in FIG. 11b. The semiconductor substrate 60 is, in advance, formed with a plurality of electrode portions 61 arranged at a predetermined pitch and a protective film 62 for protecting the obverse surface of the substrate. The electrode portions 61 comprise part of an Al wiring pattern or a Cu wiring pattern formed on the obverse surface of semiconductor substrate 60. The protective film 62 includes openings 62a at locations corresponding to the electrode portions 61. The conductor film 63 is formed by applying Ti, Ni or Cu by sputtering or vapor deposition to cover the surfaces of the electrode portions 61 and the protective film 62.
Subsequently, as shown in FIG. 11c, a resin film 64 is formed on the semiconductor substrate 60. Specifically, a photosensitive liquid resin composite is applied to the semiconductor substrate 60 by spin-coating.
Then, as shown in FIG. 12a, openings 64a are formed in the resin film 64. Specifically, the openings 64a are formed in the resin film 64 at locations corresponding to the electrode portions 61 by a light-exposure process using a predetermined mask (not shown) and the subsequent developing process.
Subsequently, as shown in FIG. 12b, barrier metal layers 65 are formed at the openings 62a and the openings 64a by electroplating. The barrier metal layers 65 are provided to prevent the wiring material of the electrode portions 61 from diffusing toward solder bumps which will be described later and to prevent the solder component of the solder bumps from diffusing toward the electrode portions 61. Instead of the electroplating, the barrier metal layers may be formed by electroless plating, as disclosed in JP-A-6-140409, for example.
Then, as shown in FIG. 12c, solder plating 66 as a bump material is deposited at each of the openings 64a by electroplating.
Subsequently, as shown in FIG. 13a, the protective film 64 is removed by using a predetermined stripping agent. Then, as shown in FIG. 13b, the exposed portions of the conductor film 63 are etched away. Then, as shown in FIG. 13c, the solder plating 66 is heated for temporary melting, thereby providing solder bumps 66xe2x80x2.
In the above-described prior art method, the solder plating 66, which is the bump material, is applied to the openings 64a of the resin film 64 by electroplating. As shown in FIG. 12c, the solder plating 66 deposited by electroplating partially rides on the resin film 64, thereby having an overhung configuration. Thus, the solder plating 66 includes overhung portions 66a riding on the resin film 64. Therefore, in the process step described with reference to FIG. 13a, the overhung portions 66a may hinder the proper removal of the resin film 64. Specifically, since part of the resin film 64 is sandwiched between the overhung portions 66a and the conductor film 63 formed on the semiconductor chip 60, the removal of the resin film 64 often becomes insufficient. When the resin film 64 remains, it hinders the etching for removal of the conductor film 63 described with reference to FIG. 13b and the formation of the solder bumps 66 described with reference to FIG. 13c. When the formation of the solder bumps 66xe2x80x2 is hindered, the height uniformity of the solder bumps 66xe2x80x2 tends to be deteriorated.
Instead of the above-described electroplating which utilizes the resin film 64 having openings 64a as a mask, the solder bumps 66xe2x80x2 may be formed by a metal mask printing method. First, in the metal mask printing method, a metal mask, which is formed with a plurality of openings in advance, is prepared. The openings are provided at locations corresponding to the electrode portions of the semiconductor chip. A barrier metal layer is formed at each of the electrode portions in advance by photolithography for example. Then, the metal mask is disposed on the semiconductor chip while positioning the openings of the metal mask correspondingly to the electrode portions of the semiconductor chip. Subsequently, solder paste containing solder powder is applied to the openings of the metal mask by a printing method. Then, after the metal mask is removed from the surface of the semiconductor chip, the solder powder in the solder paste is temporarily melted by heating. As a result, generally spherical solder bumps are formed on the electrode portions of the semiconductor chip. This technology is disclosed in JP-A-11-340270 for example.
However, in the metal mask printing method, when the metal mask is to be disposed on the semiconductor chip, the openings need be positioned correspondingly to the electrode portions. Such positioning becomes more difficult as the arrangement pitch of the electrode portions becomes smaller. Particularly when the arrangement pitch is no more than 200 xcexcm, the positional deviation in disposing the metal mask becomes significantly large. The positional deviation of the metal mask affects the position of the bump formation, which may lead to a conduction failure when the semiconductor chip is flip-chip bonded to a wiring board.
Moreover, in the metal mask printing method, the metal mask need be removed from the semiconductor chip before heating the solder paste. At that time, part of the solder paste is often removed together with the metal mask. Particularly, the smaller the diameter of the electrodes and hence of the openings of the metal mask is, the larger the proportion of the removed amount of the solder paste in the entire solder paste is. Such partial removal of the solder paste makes it difficult to form solder bumps having a proper size, which problem becomes more serious as the diameter of the electrodes decreases for providing a minute wiring pattern.
Further, in the metal mask printing method, the solder paste is subjected to the heating treatment after the metal mask is removed from the semiconductor chip. Therefore, the solder paste on the electrodes is likely to flow during the heating due to the decrease of the viscosity. As a result, one deposit of the solder paste may join with an adjacent deposit of the solder paste. In such a case, short-circuiting occurs between the adjacent solder bumps. Such a problem is more likely to occur, as the arrangement pitch of the electrodes becomes smaller.
In this way, with the metal mask printing method, it is difficult to form bumps highly accurately on a semiconductor chip provided with electrodes arranged at a minute pitch.
In the technique disclosed in JP-A-11-340270 described above, instead of a metal mask, a polyimide mask is used for defining openings for applying the solder paste. However, as described in JP-A-11-340270, the polyimide mask is not removed from the semiconductor chip. When the polyimide mask remains around the solder bumps on the semiconductor chip, an under-filling material cannot be properly loaded between the semiconductor chip and the wiring board in flip-chip bonding the semiconductor chip to the wiring board. Thus, the polyimide mask hinders the loading of the under-filling material between the semiconductor chip and the wiring board. Therefore, it may be difficult to provide reliable connection between the semiconductor chip and the wiring board.
The present invention, which is conceived under these circumstances, relates to a semiconductor device making method which is capable of forming bumps highly accurately at electrode portions arranged at a minute pitch and is capable of providing a semiconductor device which can be connected to a connection object with high reliability.
According to the present invention, there is provided a method of making a semiconductor device, which comprises a resin film forming step for forming a resin film on a semiconductor substrate provided with electrode portions to cover the electrode portions, an opening forming step for forming openings in the resin film at locations corresponding to the electrode portions, a loading step for loading a bump material in the openings, a bump forming step for forming bumps in the openings by heating, and a removing step for removing the resin film.
With such a semiconductor device making method, bumps can be formed highly accurately at electrode portions arranged at a minute pitch.
In the present invention, the openings for loading the bump material may be formed in the resin film by photolithography or UV-YAG laser application, for example. By the photolithography or the UV-YAG laser application, openings can be formed in the resin film at a minute pitch corresponding to the electrodes with positional accuracy. Therefore, the bump material can be applied to each of the electrode portions with high positional accuracy even when the electrodes are arranged at a minute pitch. Thus, according to the present invention, bumps can be formed highly accurately at the electrode portions on the semiconductor substrate.
The resin film of the present invention may be dissolved or swelled, for example, by the use of an appropriate solvent after the bumps are formed. Therefore, the present invention can avoid such a problem as partial removal of the bump material or the solder paste, which may occur in the metal mask printing method in which a metal mask need be removed before bumps are formed.
Further, in the bump forming process accompanying the heating treatment, the bumps are made with the deposits of the bump material separated from each other by the resin film remaining on the semiconductor substrate. Therefore, short-circuiting does not occur between adjacent bumps.
In this way, according to the present invention, it is possible to supply an appropriate amount of bump material to each of the electrode portions positionally accurately and to prevent short-circuiting between adjacent solder bumps. Therefore, solder bumps can be formed highly accurately at electrode portions arranged at a small pitch.
According to the present invention, a semiconductor device is provided which can be connected to a connection object with high connection reliability.
According to the present invention, the resin film provided as a mask for forming bumps is removed. The resin film is removed after the bump material loaded in the openings is heated to provide bumps. Even when the bump material after the loading step has an overhung configuration, the overhung portion tends to disappear due to the surface tension when the bump material is heated to become bumps. Therefore, according to the present invention, the resin film provided for bump formation can reliably be removed. Since the resin film for bump formation does not remain, after the semiconductor chip is mounted to a connection object such as a wiring board, a sealing resin and an under-filling material can properly be loaded between the semiconductor chip and the connection object. Since the sealing resin and the under-filling material protect the connecting portions, high connection reliability is provided between the semiconductor chip and the connection object.
In this way, according to the present invention, it is possible to form bumps highly accurately on electrode portions arranged at a minute pitch and to provide a semiconductor device which can be connected to a connection object with high connection reliability.
In a preferred embodiment, the method of making a semiconductor device of the present invention further comprises the step of forming a barrier metal layer on each of the electrode portions by electroless plating before the resin film forming step. In the opening forming step, the openings are formed in the resin film to expose the barrier metal layers. With this method, it is unnecessary to form a conductor film for providing barrier metal layers by electroplating. Accordingly, it is also unnecessary to etch away the conductor film. Thus, since the formation and the removal of the conductor film for electroplating are unnecessary, the efficiency for manufacturing a semiconductor device is enhanced.
In another preferred embodiment, the method further comprises the step of forming a barrier metal layer on each of the electrode portions by electroless plating after the opening forming step. Also with this method, the formation and the removal of the conductor film for electroplating are unnecessary so that the efficiency for manufacturing a semiconductor device is enhanced. Further, with this method, the resin film for forming openings does not come into contact with the upper surface of the barrier metal layer. Therefore, good electrical connection can be provided between the barrier metal layers and the bumps formed thereon.
Preferably, the barrier metal layer forming step includes the steps of forming a catalyst layer on the electrode portion, forming an electroless nickel plating layer having a composition of Nixe2x80x94P, Nixe2x80x94B or Nixe2x80x94Pxe2x80x94B on the catalyst layer, and forming an electroless gold plating layer or an electroless palladium plating layer on the electroless nickel plating layer. In this case, it is preferable that the catalyst layer contains Zn or Pd. With such a method, good barrier metal layers can be formed.
Preferably, the bump material is solder paste containing solder powder containing a metal selected from the group consisting of Sn, Pb, Cu, Ag, In, Zn, Bi, Sb and Au. In this case, the supplying of the solder material may be performed by loading the bump material into the openings using a squeegee. Preferably, the loading with the use of a squeegee may be performed twice or more.
In another preferred embodiment, the method further comprises the steps of forming a conductor film on the semiconductor substrate to cover the electrode portions before the resin film forming step and forming a barrier metal layer on each of the electrode portions by electroplating after the opening forming step. In the loading step, the bump material is deposited onto the barrier metal layer by electroplating.
Preferably, in the present invention, the resin film forming step comprises bonding a film of photosensitive resin material as the resin film to the semiconductor substrate. With this method, it is possible to use a film of resin material having a thickness which has been controlled to be equal to that of a resin film to be formed. Therefore, the thickness control of a resin film to be formed on the semiconductor substrate can be performed easily. Further, a relatively thick resin film can be easily formed as compared with the case where resin material in liquid state is used. To load a sufficient amount of solder paste into the openings formed in the resin film, it is preferable that the resin film has a film thickness of no less than 30 xcexcm. Moreover, when the resin film is photosensitive, the openings can be formed by photolithography. By the photolithography, openings can be formed in the resin film at a minute pitch with positional accuracy.
Preferably, in the removing step, the resin film is removed by using a stripping agent having a pH of 8-13. Further, preferably, the stripping agent contains amine. It is preferable that the stripping agent contains a corrosion inhibitor for preventing the bumps from corroding. Further, preferably, the stripping agent contains a corrosion inhibitor for preventing the barrier metal layers and the electrode portions from corroding. With such a method, the removal of the resin film can be performed reliably.
Preferably, the method further comprises the steps of covering the bumps with a flux or carboxylic acid and heating the bumps for temporary melting. When the bumps are heated for temporary melting while being covered with a flux or carboxylic acid, the configuration of the bumps can be adjusted. This further enhances the accuracy of the bump formation.